Parkes observations for project P456 semester 2018APRS_26

The Parkes Pulsar Timing Array (PPTA) project has three primary goals: (a) detection of gravitational waves from astronomical sources, (b) establishment of a pulsar timescale, and (c) improvement of our understanding of Solar-system dynamics. The PPTA is the oldest of three international pulsar timing groups. We have the smallest telescope and the smallest group, but the best measurements and the best results. Our bound on the strength of the incoherent gravitational wave background is the only bound which significantly constrains theoretical models. We have maintained our leading position because: we have the southern sky; we have a small but well-focussed group; we have the best-calibrated receivers; and we have been able to observe with an almost regular cadence of 15 to 20 days at three different wavelengths. With this proposal we aim to maintain our pre-eminent position in the field.\r\n\r\nUnlike most observing proposals, this is a continuing proposal for which the observations will continue to improve bounds on ultra-low-frequency gravitational waves until they are finally detected. Continued Parkes observations will remain valuable at least until the first stage of the SKA is able to improve on our sensitivity and observing cadence. Even after the gravitational wave background is detected we will want to continue observations in support of the nascent field of gravitational wave astronomy!

帕克斯脉冲星计时阵列（Parkes Pulsar Timing Array, PPTA）项目拥有三大核心目标：（a）探测来自天体源的引力波；（b）建立脉冲星时标；（c）深化对太阳系动力学的认知。PPTA是三大国际脉冲星计时研究组中历史最悠久的一个。我们的望远镜与研究团队规模均为三者中最小，但却获得了最优质的观测数据与研究成果。我们针对非相干引力波背景强度给出的约束结果，是目前唯一能对相关理论模型构成显著限制的成果。我们能够始终保持领域领先地位的原因在于：我们拥有南天球观测窗口；拥有一支精干且目标聚焦的研究团队；配备了经过最优校准的接收系统；并且能够以近乎固定的15至20天观测周期在三个不同波段开展观测。通过本申请，我们旨在维持本领域的领先地位。

与多数观测申请不同，本项目属于持续性观测计划，相关观测将持续优化超低频引力波背景的约束精度，直至最终成功探测到这类引力波信号。至少在平方公里阵列（Square Kilometre Array, SKA）一期工程能够在观测灵敏度与周期上超越我们当前的水平之前，帕克斯天文台的持续观测仍将具备重要科学价值。即便引力波背景被成功探测，我们仍需继续开展观测，以支撑新兴的引力波天文学领域发展。